Transverse Heterogeneity Effects in the Dissipation-Induced Instability of a Horizontal Porous Layer

2011 ◽  
Vol 133 (12) ◽  
Author(s):  
A. Barletta ◽  
M. Celli ◽  
A. V. Kuznetsov

The linear stability of a parallel flow in a heterogeneous porous channel is analyzed by means of the Darcy law and the Oberbeck–Boussinesq approximation. The basic velocity and temperature distributions are influenced by the effect of the viscous dissipation, as well as, by the boundary conditions. A horizontal porous layer bounded by impermeable and infinitely wide walls is considered. The lower boundary is assumed to be thermally insulated, while the upper boundary is assumed to be isothermal. A transverse heterogeneity for the permeability and for the thermal conductivity is taken into account. The main task of this work is to investigate the role of this heterogeneity in changing the threshold for the onset of instability. A linear stability analysis by means of the normal modes method is performed. The onset of instability against oblique rolls is studied. The eigenvalue problem is solved numerically.


2011 ◽  
Vol 679 ◽  
pp. 544-558 ◽  
Author(s):  
D. A. NIELD ◽  
A. BARLETTA ◽  
M. CELLI

The linear stability of a basic forced and free convection flow in an inclined porous channel is analysed by using the Darcy law and the Oberbeck–Boussinesq approximation. The basic velocity and temperature distributions are influenced by the effect of viscous dissipation, as well as by the boundary conditions. The boundary planes are assumed to be impermeable and isothermal, with a temperature of the lower boundary higher than that of the upper boundary. The instability against longitudinal rolls is studied by employing a second-order weighted residual solution and an accurate sixth-order Runge–Kutta solution of the disturbance equations. The instability against transverse rolls is also investigated. It is shown that these disturbances are in every case less unstable than the longitudinal rolls.



Fluids ◽  
2021 ◽  
Vol 6 (12) ◽  
pp. 450
Author(s):  
Pedro Vayssière Brandão ◽  
Michele Celli ◽  
Antonio Barletta

The onset of the thermal instability is investigated in a porous channel with plane parallel boundaries saturated by a non–Newtonian shear–thinning fluid and subject to a horizontal throughflow. The Ellis model is adopted to describe the fluid rheology. Both horizontal boundaries are assumed to be impermeable. A uniform heat flux is supplied through the lower boundary, while the upper boundary is kept at a uniform temperature. Such an asymmetric setup of the thermal boundary conditions is analysed via a numerical solution of the linear stability eigenvalue problem. The linear stability analysis is developed for three–dimensional normal modes of perturbation showing that the transverse modes are the most unstable. The destabilising effect of the non–Newtonian shear–thinning character of the fluid is also demonstrated as compared to the behaviour displayed, for the same flow configuration, by a Newtonian fluid.



2009 ◽  
Vol 131 (10) ◽  
Author(s):  
I. S. Shivakumara ◽  
C. E. Nanjundappa ◽  
M. Ravisha

The onset of thermomagnetic convection in a ferrofluid saturated horizontal porous layer in the presence of a uniform vertical magnetic field is investigated for a variety of velocity and temperature boundary conditions. The Brinkman–Lapwood extended Darcy equation, with fluid viscosity different from effective viscosity, is used to describe the flow in the porous medium. The lower boundary of the porous layer is assumed to be rigid-ferromagnetic, while the upper boundary is considered to be either rigid-ferromagnetic or stress-free. The thermal conditions include fixed heat flux at the lower boundary, and a general convective-radiative exchange at the upper boundary, which encompasses fixed temperature and heat flux as particular cases. The resulting eigenvalue problem is solved using the Galerkin technique and also by using regular perturbation technique when both boundaries are insulated to temperature perturbations. It is found that the increase in the Biot number and the viscosity ratio, and the decrease in the magnetic as well as in the Darcy number is to delay the onset of ferroconvection. Besides, the nonlinearity of fluid magnetization has no effect on the onset of convection in the case of fixed heat flux boundary conditions.



2005 ◽  
Vol 62 (5) ◽  
pp. 1545-1559 ◽  
Author(s):  
Riwal Plougonven ◽  
David J. Muraki ◽  
Chris Snyder

Abstract Normal modes of a linear vertical shear (Eady shear) are studied within the linearized primitive equations for a rotating stratified fluid above a rigid lower boundary. The authors' interest is in modes having an inertial critical layer present at some height within the flow. Below this layer, the solutions can be closely approximated by balanced edge waves obtained through an asymptotic expansion in Rossby number. Above, the solutions behave as gravity waves. Hence these modes are an example of a spatial coupling of balanced motions to gravity waves. The amplitude of the gravity waves relative to the balanced part of the solutions is obtained analytically and numerically as a function of parameters. It is shown that the waves are exponentially small in Rossby number. Moreover, their amplitude depends in a nontrivial way on the meridional wavenumber. For modes having a radiating upper boundary condition, the meridional wavenumber for which the gravity wave amplitude is maximal occurs when the tilts of the balanced edge wave and gravity waves agree.



Author(s):  
Pedro Vayssière Brandão ◽  
Michele Celli ◽  
Antonio Barletta

The onset of the thermal instability is investigated in a porous channel with plane parallel boundaries saturated by a non–Newtonian shear–thinning fluid and subject to a horizontal throughflow. The Ellis model is adopted to describe the fluid rheology. Both horizontal boundaries are assumed to be impermeable. A uniform heat flux is supplied through the lower boundary, while the upper boundary is kept at a uniform temperature. Such an asymmetric setup of the thermal boundary conditions is analysed via a numerical solution of the linear stability eigenvalue problem. The linear stability analysis is developed for three–dimensional normal modes of perturbation showing that the transverse modes are the most unstable. The destabilising effect of the non-Newtonian shear–thinning character of the fluid is also demonstrated as compared to the behaviour displayed, for the same flow configuration, by a Newtonian fluid.



2019 ◽  
pp. 22-29
Author(s):  
Н. В. Фрадкіна

The purpose and tasks of the work are to analyze the contemporary Ukrainian mass culture in terms of its value and humanistic components, as well as the importance of cultural studies and Ukrainian studies in educational disciplines for the formation of a holistic worldview of modern youth.Analysis of research and publications. Scientists repeatedly turned to the problems of the role of spirituality in the formation of society and its culture. This problem is highlighted in the publications by O. Losev, V. Lytvyn, D. Likhachev, S. Avierintsev, M. Zakovych, I. Stepanenko and E. Kostyshyn.Experts see the main negative impact of mass culture on the quality approach, which determines mass culture through the market, because mass culture, from our point of view, is everything that is sold and used in mass demand.One of the most interesting studies on this issue was the work by the representatives of Frankfurt School M. Horkheimer and T. Adorno «Dialectics of Enlightenment» (1947), devoted to a detailed analysis of mass culture. Propaganda at all socio-cultural levels in the form is similar in both totalitarian and democratic countries. It is connected, according to the authors, with the direction of European enlightenment. The tendency to unify people is a manifestation of the influence of mass culture, from cinema to pop. Mass culture is a phenomenon whose existence is associated with commerce (accumulation in any form – this is the main feature of education), in general, the fact that it exists in this form is related to the direction of the history of civilization.Modern mass culture, with its externally attractive and easily assimilated ideas and symbols, appealing to the trends of modern fashion, becomes a standard of prestigious consumption, does not require intense reflection, allows you to relax, distract, not teach, but entertains, preaches hedonism as the main spiritual value. And as a consequence, there are socio-cultural risks: an active rejection of other people, which leads to the formation of indifference; cruelty as a character trait; increase of violent and mercenary crime; increase in the number of alcohol and drug addicts; anti-patriotism; indifference to the values of the family and as a result of social orphanhood and prostitution.Conclusions, perspectives of research. Thus, we can conclude that modern Ukrainian education is predominantly formed by the values of mass culture. Namely, according to the «Dialectic» by Horkheimer and Adorno, «semi-enlightenment becomes an objective spirit» of our modern society.It is concluded that only high-quality education can create the opposite of the onset of mass culture and the destruction of spirituality in our society. It is proved that only by realizing the importance of cultivating disciplines in the educational process and the spiritual upbringing of the nation, through educational reforms, humanitarian knowledge will gradually return to student audiences.Formation of youth occurs under the influence of social environment, culture, education and self-education. The optimal combination of these factors determines both the process of socialization itself and how successful it will be. In this context, one can see the leading role of education and upbringing. It turns out that the main task of modern education is to spread its influence on the development of spiritual culture of the individual, which eventually becomes a solid foundation for the formation of the individual. Such a subject requires both philosophical and humanitarian approaches in further integrated interdisciplinary research, since the availability of such research will provide the theoretical foundation for truly modern educational and personal development.



2016 ◽  
Vol 13 (2) ◽  
pp. 86-99
Author(s):  
Vimbai Moreblessing Matiza

Dramatic and theatrical performances have a long history of being used as tools to enhance development in children and youth. In pre-colonial times there were some forms of drama and theatre used by different communities in the socialisation of children. It is in the same vein that this article, through the Intwasa koBulawayo performances, seeks to evaluate how drama and theatre are used to nurture children and youth into different developmental facets of their lives. The only difference which this article will take into cognisance is that the performances are done in a different environment, which is not the one used in the pre-colonial times. Although these performances were like this, the most important factor is the idea that children and youth are socialised through these performances. It is also against this backdrop that children and youth are growing up in a globalised environment, hence the performances should accommodate people from all walks of life and teach them relevant issues pertaining to life as they live it now. Thus the main task of the article is to spell out the role of drama and theatre in the nurturing of children and youth through socio economic and political development in Intwasa koBulawayo festivals.



Author(s):  
Fajar Syahputra ◽  
Mesran Mesran ◽  
Ikhwan Lubis ◽  
Agus Perdana Windarto

The teacher is a major milestone in the world of education, the ability and achievement of students cannot be separated from the role of a teacher in teaching and guiding students. Based on the Law of the Republic of Indonesia No. 14 of 2005 concerning Teachers and Lecturers, in Article 1 explained that teachers are professional educators with the main task of educating, teaching, guiding, directing, training, evaluating, and evaluating students in early childhood education through formal education, basic education and education medium. Whereas in Article 4 of the Act, it is explained that the position of teachers as professionals serves to enhance the dignity and role of teachers as learning agents to function to improve the quality of national education.Decision making is an election process, among various alternatives that aim to meet one or several targets. The decision-making system has 4 phases, namely intelligence, design, choice and implementation. These phases are the basis for decision making, which ends with a recommendation.The Preferences Selection Index (PSI) method is a rarely used decision support system method. This method is a method developed by stevanie and Bhatt (2010) to solve the Multi Criteria Decision Making (MCDM). With the right consideration, this method can be one of the tools to determine policies in decision-making systems, especially the selection of outstanding teachers. Determination of policies taken as a basis for decision making, must use criteria that can be defined clearly and objectively.Keywords: Decision Support System, PSI, Selection of Achieving Teachers



2020 ◽  
pp. 77-82
Author(s):  
Anna Dedurina

In recent years, manual therapy has been increasingly used. This was facilitated by the scientific justification of the method, wellestablished training of specialists, good results of manual diagnostics and therapy of patients. Manual medicine is a system of diagnostic and therapeutic manual techniques aimed at identifying and treating disorders of the musculoskeletal system, manifested in the form of functional joint blockages, hypermobility and regional postural muscle imbalance. In addition to nosological diagnosis, manual examination data are of great importance for successful treatment. Manual diagnostics is a method aimed at detecting disorders in the spine, muscles and joints, as well as ligaments of the human body. The main task of diagnostics is to establish a differential diagnosis between diseases of the spine and joints and other nosological forms. Timely manual diagnostics with the use of manual therapy technologies helps to increase the effectiveness of complex treatment and helps to avoid complications and disability at an early age.



2021 ◽  
pp. 1357034X2110256
Author(s):  
Denisa Butnaru

Motility impairments resulting from spinal cord injuries and cerebrovascular accidents are increasingly prevalent in society, leading to the growing development of rehabilitative robotic technologies, among them exoskeletons. This article outlines how bodies with neurological conditions such as spinal cord injury and stroke engage in processes of re-appropriation while using exoskeletons and some of the challenges they face. The main task of exoskeletons in rehabilitative environments is either to rehabilitate or ameliorate anatomic functions of impaired bodies. In these complex processes, they also play a crucial role in recasting specific corporeal phenomenologies. For the accomplishment of these forms of corporeal re-appropriation, the role of experts is crucial. This article explores how categories such as bodily resistance, techno-inter-corporeal co-production of bodies and machines, as well as body work mark the landscape of these contemporary forms of impaired corporeality. While defending corporeal extension rather than incorporation, I argue against the figure of the ‘cyborg’ and posit the idea of ‘residual subjectivity’.



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